Power outages potentially create unsafe conditions within buildings. Spaces that have no natural light are difficult for people to move in during power outages. If the power outage is a result of some other dangerous condition such as a fire or an earthquake, not only must the halls be lit, but exit signs must remain illuminated as well. Accordingly, both safety codes and common sense require that some sort of backup power be available to provide for at least tens of minutes, power to these safety-critical devices.
Rechargeable batteries are the industry standard for backup power sources. They are relatively compact and have storage capacity to provide operating power for signs or lights for at least as long codes require. But batteries are not environmentally friendly, require recharging at regular intervals, and eventually deteriorate to the point of requiring replacement.
The potential for deterioration of such batteries requires their periodic testing to assure that they can provide adequate emergency power. The need for this testing is itself a further disadvantage of battery backup power.
Accordingly, a backup power unit that provides adequate backup power, requires no periodic charging, has an indefinite service life, and quickly indicates if the unit has failed, would be a boon to building managers.